In a recent wireless communication system, an auto repeat request (ARQ) scheme or a hybrid auto repeat request (HARQ) scheme is mainly used to improve throughput, thereby enabling desirable communication.
According to the ARQ or HARQ scheme, a receiving side feeds the presence of error in received data back to a transmitting side, so that the transmitting side can perform data retransmission when any error is found in the received data. In other words, according to the ARQ or HARQ scheme, after the transmitting side transmits data to the receiving side, the receiving side transmits a positive acknowledgement signal (ACK) to the transmitting side if it receives the transmitted data without any error whereas the receiving side transmits a negative acknowledgement signal (NACK) to the transmitting side if any error is found in the received data, whereby the transmitting side retransmits data to allow the receiving side to exactly receive the data:
FIG. 1 illustrates a hybrid ARQ (HARQ) scheme in WCDMA system according to the related art. In FIG. 1, a base station determines a user equipment which will receive a packet and formats (coding rate, modulation mode, data quantity, etc.) of the packet, which are to be transmitted to the user equipment, and reports information related to the determined formats to the user equipment through a downlink control channel (HS-SCCH) and transmits corresponding data packets (HS-DSCH) at this time. The user equipment can identify formats of the packet to be transmitted thereto and a transmission timing point by receiving the downlink control channel, and can receive the packet by using the identified results.
After receiving the packet, the user equipment decodes the received packet. If decoding is successfully performed, the user equipment transmits ACK to the base station. The base station which has received ACK recognizes that packet transmission to the user equipment has been successfully performed, and then performs next packet transmission. If the user equipment fails to decode the packet, the user equipment transmits NACK to the base station, and the base station which has received NACK recognizes that packet transmission to the user equipment has been failed and configures the same data in the same packet type or a new packet type at a proper timing point to perform retransmission. At this time, the user equipment combines the retransmitted packet with the packet, which have been previously received but failed in decoding, in various manners to try decoding again.
In a wireless communication system which uses a multicarrier mode such as orthogonal frequency division multiplexing (OFDM) or a single carrier-frequency division multiple access (SC-FDMA), radio resources are a set of continuous sub-carriers and are defined by a time-frequency region of a two-dimensional sphere. In this case, when the HARQ scheme is used, radio resources for transmission of control information and retransmission data for HARQ should be allocated efficiently to avoid their waste.